The present invention relates to a spindle clamper for a machine tool, and, more particularly, to a device for clamping two coaxial spindles of a machine tool, such as boring and milling spindles of a horizontal boring and milling machine.
Various spindle clamping devices are used for spindles of machine tools, wherein a hollow first spindle is rotatably supported in a spindle head and a second spindle is rotatably supported in the hollow first spindle so as to be movable back and forth in the axial direction thereof. In the case of horizontal boring and milling machines, in which the first spindle is a milling spindle and the second spindle is a boring spindle, clamping devices for the machine tools can be broadly divided into two types (1) and (2) which are as follows:
(1) Pressurized oil is supplied into a thin shell ring (which is similar to clamp rings described in Japanese Utility Model Publication No. Sho 62-43684) between a milling spindle rotatably supported in a spindle head and a boring spindle rotatably supported in the milling spindle to be movable back and forth in the axial direction of the boring spindle, to clamp the boring spindle to the milling spindle. -;hen the pressurized oil is discharged from the thin shell ring, the two spindles are unclamped.
(2) A function of self-retaining pressurized oil is provided in the second spindle, that is, the boring spindle, as described in the Publication mentioned above, to clamp the milling and the boring spindles to each other. More specifically, a thin shell ring is provided between the milling spindle rotatably supported by the spindle head and the boring spindle rotatably supported in the milling spindle to be movable back and forth in the axial direction of the boring spindle An accumulator is provided to supply pressurized oil into the shell ring. An oil injection nozzle unit is provided for the accumulator, and a hydraulic oil supply unit is provided to supply oil to the injection nozzle.
As for the type (1), the pressurized oil must be always supplied or retained during the rotation of the spindles. For that reason, if the milling spindle is rapidly rotated for machining, much heat is generated at a static pressure pocket during the rotation so as to elongate the boring spindle in the axial direction thereof by thermal expansion, thereby adversely affecting the accuracy of the machining.
As for the type (2), leakage of the pressurized oil cannot be prevented during the rotation of the spindles, and the machine tool therefore cannot be operated for a long time. For that reason, machining must be stopped, the boring spindle must be positioned again at a prescribed angle, and the oil injection nozzle unit and the hydraulic oil supply unit must be matched with each other in phase, before the operation for supplying the pressurized oil into the thin shell ring is carried out. With the leakage of the pressurized oil, the pressure of the oil to be applied to the thin shell ring will drop so that it becomes difficult to securely clamp the spindles to each other with high rigidity. Moreover, since it takes some time to do the work for supplying the pressurized oil into the thin shell ring, the rate of operation of the machine tool is lowered.